2004-2009 Honda TRX450R/TRX450ER Service Manual, Page 203Get this manual
CYLINDER HEADVALVE
CYLINDER COMPRESSION
Warm the engine to normal operating temperatureStop the engine and remove the spark plug (page 49)Install the compression gauge into the spark plug holeShift the transmission in neutralOpen the throttle all the way and operate the kickstarter forcefully several times until the gauge reading stops risingThe cylinder COMPRESSION PRESSURE: compression '04'05: specification is 745 kPa (7.6 kgfcm2,108 psi) comparatively low After '05: because the TRX450ER; camshaft has 343382 kPa (3.53.9 kgfcm2, 5056 psi) decompression TRX450R; device installed2 COMPRESSION GAUGE
9611000 kPa (9.810.2 kgfcm ,139145 psi)
Low compression can be caused by:blown cylinder head gasketimproper valve adjustmentvalve leakageworn piston ring or cylinder High compression can be caused by:carbon deposits in combustion chamber or on piston head